This invention relates to displacement machines for compressible media and, more particularly, to a new and improved displacement machine having a more effective and reliable structural arrangement.
Displacement machines for compressible media having a spiral displacement chamber formed by a housing having a base with an upstanding spiral wall and a rotor formed with another upstanding wall which can be driven eccentrically to the housing are known in principle, for example, from DE-OS No. 31 07 231. Such machines provide for nearly pulsation-free flow of a gaseous working medium such as air or an air/fuel mixture and they can therefore be utilized to advantage, among other things, to supply such mixtures to internal combustion engines, in particular in passenger automobiles. When such displacement machines are operated as a pump or a compressor, a plurality of approximately sickle-shaped working spaces are generally enclosed between the spiral walls of the housing and the rotor. These working spaces extend from a working medium inlet through the displacement chamber to a working medium discharge. During movement of the rotor, the volume of the working spaces can also be continuously reduces so that the pressure of the working medium is correspondingly increased.
The displacement bodies are formed by spiral-shaped ridges which are disposed essentially perpendicularly on the base of the disc-shaped rotor and they are relatively long in the direction away from the base in relation to their thickness. The housing has a similar arrangement between the displacement chambers, where the chamber walls comprise ridges upstanding which are spiral-shaped and are relatively long in the direction away from the base in relation to the wall thickness. During operation of the displacement machine, these relatively narrow ridges providing the displacement chamber walls come nearly in contact with the base portions of the housing and the rotor so that the sickle-shaped working spaces formed between the ridges are sealed relative to one another. The closer the ridges come to the base portions, the better is the sealing of the working spaces relative to one another and thus the output of the displacement machine is increased. On the other hand, a butting or direct contact between the components is to be avoided as much as possible because of the danger of damage. Therefore, the housings and rotors of displacement machines operating according to the spiral principle must be produced with very high precision and with narrow recesses between the peripheral contours of the displacement bodies and the displacement chamber walls.
It has been found, however, that even if high precision and narrow tolerances are adhered to during manufacture with a view to providing such small recesses between the displacement bodies and the displacement chamber walls, butting or direct contact problems may occur between the housing and the rotor because of different thermal expansion of the components. It is known that the foot regions of the radially outer peripheral walls of the displacement bodies tend to butt against the inner contours of the radially outer walls of the associated displacement chambers of the housing. This occurs primarily because the rotor carrying the ridges which provide the displacement bodies is evidently heated to a higher temperature than the housing during operation and, as a result, the rotor walls expand more than the walls of the housing forming the displacement chambers. Specifically, butting of the radially outer displacement bodies against the inward walls of the displacement chambers was found in certain peripheral regions of the machine which were located approximately in the mid-angle region between a center line connecting the centers of the housing and of the bearing bore fixed in the housing for eccentric bearing of the rotor and a line extending perpendicularly thereto through the housing center. Although a general increase in the clearance between the peripheral contours of the displacement bodies and the displacement chamber walls would reduce the danger of butting or contact, it would also cause substantial output losses of the displacement machine due to increased leakage.